Optical waveguide devices each using an electro-optic crystal such as a LiNbO3 (LN) substrate and a LiTaO2 substrate have been developed. In order to form such an optical waveguide device, an optical waveguide is first formed in such a manner that a metal film made of titanium or the like is formed and thermally diffused on a part of a crystal substrate or is subjected to proton exchange under benzoic acid after being patterned. With provision of electrodes near the optical waveguide, the optical waveguide device is formed. An example of such an optical waveguide device includes an optical modulator.
An optical modulator is accommodated in a metal package and mounted in a transmitter as an optical modulator module. Recently, various surface-mounting type components have been developed for the purpose of improving mounting performance (see, for example, Patent Document 1). However, they give rise to a problem in high-frequency characteristics.
Patent Document 2 discloses a configuration in which a spacer is interposed between a package and a flexible substrate to alleviate impedance mismatching. Patent Document 3 discloses a configuration in which a lead pin is mounted parallel on the signal electrode pad of an FPC and solder-connected.    Patent Document 1: Japanese Laid-open Patent Publication No. 4-336702    Patent Document 2: Japanese Laid-open Patent Publication No. 2007-42756    Patent Document 1: Japanese Laid-open Patent Publication No. 2009-252918
However, the configurations of Patent Documents 2 and 3 put limitations on space.